1. Field of the Invention
The present invention relates to a gas processing method, such as a method of forming a film by chemical vapor deposition, a gas processing apparatus for carrying out the gas processing method, and an integrated valve unit to be incorporated into such a gas processing apparatus.
2. Description of the Related Art
A film of a metal or a metal compound, such as W (tungsten), WSi (tungsten silicide), Ti (titanium), TiN (titanium nitride), TiSi (titanium silicide) or the like, is deposited to form a wiring pattern on semiconductor wafer (hereinafter referred to simply as “wafer”), i.e., a workpiece, or to fill up holes between wiring lines in a semiconductor device manufacturing process. When depositing a WSi film, WF6 gas (tungsten hexafluoride gas), SiH4 gas (silane gas) or SiH2Cl2 gas (dichlorosilane gas) is used as a process gas.
When forming a WSi film, a mixture of the process gas and a carrier gas is supplied into a processing chamber, and a wafer placed in the processing chamber is heated to react the same with the process gas. In an initial stage of the process, the flow rate of the WF6 gas is controlled strictly so that a desired nucleation film is formed to enable the formation of a film of an improved film quality. With this object in view, a gas processing apparatus for forming a film of an improved quality is provided with a nucleation WF6 gas supply line capable of strictly controlling the flow of WF6 gas and a deposition WF6 gas supply line.
When selecting the deposition WF6 gas supply line while the nucleation WF6 gas supply line is being used, WF6 gas remains in a downstream section of the nucleation WF6 gas supply line below a valve placed in the nucleation WF6 gas supply line. If a large amount of WF6 gas remains in the downstream section of the nucleation WF6 gas supply line, the WF6 gas is drawn out of the downstream section by the carrier gas. Consequently, WF6 gas is supplied excessively into the processing chamber and a film of a desired quality cannot be formed.